Disc drive with compensation for non-repeatable runout

Abstract

An NRRO compensation circuit controls a head position in a disc drive. The circuit has a first frequency circuit providing a first output corresponding to NRRO and a first characteristic sensing circuit that senses the first output and that generates a first control output that adjusts a first NRRO compensation gain. A first control circuit included in the NRRO compensation circuit receives the first control output and the first NRRO compensation gain and provides a first NRRO compensator output.

1. A circuit controlling a head position in an apparatus comprising:
 a runout input that includes a characteristic of non-repeatable runout (NRRO); and 
 a first frequency circuit receiving the runout input and providing a first frequency indicating output corresponding to NRRO noise; 
 a first characteristic sensing circuit sensing the first frequency-indicating output and including a noise threshold level, the first characteristic sensing circuit generating a first control output that adjusts a first NRRO compensation gain when the NRRO noise is above the noise threshold level; and 
 a first control circuit receiving the first control output and providing a first NRRO compensator output. 
 
     
     
       2. The circuit of  claim 1  wherein:
 the first frequency circuit comprises a first bandpass filter receiving a position error signal (PES) and providing a first filter output in a first preselected frequency band; 
 the first characteristic sensing circuit comprises a first gain control circuit having a first NRRO compensation gain, the first gain control circuit receiving the first filter output and providing a first NRRO compensator output to a controller; and 
 the first control circuit comprises a first amplitude sensing circuit sensing the first filter output and generating a first gain control output that adjusts the first NRRO compensation gain. 
 
     
     
       3. The circuit of  claim 2  wherein the first amplitude sensing circuit automatically tunes the first gain control output to increase the first NRRO compensation gain when the first filter output increases, and to decrease the first NRRO compensation gain when the first filter output decreases, and wherein the controller sums the position error signal and the first NRRO compensator output such that the NRRO is attenuated in the first preselected frequency band at a head position control output of the controller. 
     
     
       4. The circuit of  claim 2  wherein the first filter output has an amplitude envelope with an envelope time constant, and the first gain control output has a tuning time constant that is faster than the envelope time constant. 
     
     
       5. The circuit of  claim 2  wherein the first amplitude sensing circuit includes a recursive algorithm that tunes the first gain control output in real time. 
     
     
       6. The circuit of  claim 5  wherein the recursive algorithm is a function of 
         g   ⁡     (   t   )       =     {                 α   *     ⁢     g   ⁡     (     t   -   1     )         +       β   *     ⁡     (          e        -     e   0       )         ,       when   ⁢           ⁢        e          >     e   0                         α   *     ⁢     g   ⁡     (     t   -   1     )         ,           ⁢       when   ⁢           ⁢        e          ≤     e   0         ⁢                         
 
       where t is a number of a time increment, g is the first gain, α has a value between 0 and 1, β is a tuning rate greater than 0, e is the first filter output and e 0  is a selected level of e for turning the automatic tuning on and off. 
     
     
       7. The circuit of  claim 6  wherein the recursive algorithm has an initial condition value g(0) at the start of a seek operation, and the initial condition value g(0) is adjusted as a function of track number. 
     
     
       8. The circuit of  claim 2  wherein the first bandpass filter comprises a second order filter. 
     
     
       9. The circuit of  claim 2  wherein the controller controls the head position control output as a function of a sum of the position error signal and the first NRRO compensator output. 
     
     
       10. The circuit of  claim 2  further comprising:
 a second bandpass filter receiving the position error signal (PES) and providing a second filter output in a second preselected frequency band; 
 a second gain control circuit having a second NRRO compensation gain, the second gain control circuit receiving the second filter output and providing a second NRRO compensator output to the controller; 
 a second amplitude sensing circuit sensing the second filter output and generating a second gain control output that adjusts the second NRRO compensation gain; and 
 the controller summing the second NRRO compensator output with position error signal and the first NRRO compensator output. 
 
     
     
       11. The circuit of  claim 10  wherein the controller controls the head position control output as a function of a sum of the position error signal and the first NRRO compensator output and the second NRRO compensator output. 
     
     
       12. The circuit of  claim 10  further comprising:
 a third bandpass filter receiving the position error signal (PES) and providing a third filter output in a third preselected frequency band; 
 a third gain control circuit having a third NRRO compensation gain, the third gain control circuit receiving the third filter output and providing a third NRRO compensator output to the controller; 
 a third amplitude sensing circuit sensing the third filter output and generating a third gain control output that adjusts the third NRRO compensation gain; and 
 the controller summing the third NRRO compensator output with position error signal and the first and second NRRO compensator output. 
 
     
     
       13. The circuit of  claim 12  wherein the controller controls the head position control output as a function of a sum of the position error signal and the first NRRO compensator output and the second NRRO compensator output and the third NRRO compensator output. 
     
     
       14. A method for compensating for non-repeatable runout error (NRRO) noise in a head position, the method comprising:
 filtering to provide a first output in a first preselected frequency band; 
 providing a first NRRO compensation output as a function of the first output and a first NRRO compensation gain; and 
 sensing the first output to generate a first control output adjusting the first NRRO compensation gain when the NRRO noise is above a noise threshold level. 
 
     
     
       15. The method of  claim 14  further comprising:
 summing a position error signal and the first NRRO compensator output in a controller such that the NRRO is attenuated in the first preselected frequency band; and 
 wherein the first preselected frequency band corresponds with a first NRRO frequency peak. 
 
     
     
       16. The method of  claim 14  further comprising generating a head position control output in the controller to control the head position. 
     
     
       17. The method of  claim 14  further comprising: automatically tuning the first control output to increase when the first output increases, and to decrease when the first output decreases. 
     
     
       18. The method of  claim 17  further comprising: providing the automatic tuning with a tuning time constant that is faster than an envelope time constant of an amplitude envelope of the first output. 
     
     
       19. The method of  claim 17  further comprising: performing the automatic tuning in real time with a recursive algorithm. 
     
     
       20. The method of  claim 19  further comprising: generating the first control output as a function of: 
         g   ⁡     (   t   )       =     {                 α   *     ⁢     g   ⁡     (     t   -   1     )         +       β   *     ⁡     (          e        -     e   0       )         ,       when   ⁢           ⁢        e          >     e   0                         α   *     ⁢     g   ⁡     (     t   -   1     )         ,           ⁢       when   ⁢           ⁢        e          ≤     e   0         ⁢                         
 
       where t is time, g is the first gain, α has a value between 0 and 1, β is a tuning rate greater than 0, e is the first output and e 0  is a selected level of e for turning the automatic tuning on and off. 
     
     
       21. The method of  claim 14 , further comprising:
 filtering a position error signal (PES) to provide a second output in a second preselected frequency band; 
 amplifying the second output by a second NRRO compensation gain to provide a second NRRO compensator output to the controller; 
 sensing the second output to generate a second control output adjusting the second NRRO compensation gain; and 
 summing the second NRRO compensator output with the position error signal and the first NRRO compensator output in the controller such that the NRRO is attenuated in the second preselected frequency band. 
 
     
     
       22. The method of  claim 21  further comprising: generating a head position output in the controller to control the head position. 
     
     
       23. The method of  claim 21 , further comprising:
 filtering the position error signal (PES) to provide a third output in a third preselected frequency band; 
 amplifying the third output by a third NRRO compensation gain to provide a third NRRO compensator output to the controller; 
 sensing the third output to generate a third control output adjusting the third NRRO compensation gain; and 
 summing the third NRRO compensator output with the position error signal and the first and second NRRO compensator outputs in the controller such that the NRRO is attenuated in the second preselected frequency band. 
 
     
     
       24. The method of  claim 23  further comprising:
 generating a head position output in the controller to control the head position. 
 
     
     
       25. A circuit controlling an apparatus position, comprising:
 a summing junction providing a position error signal; 
 a controller receiving the position error signal and providing an apparatus position control output; and 
 compensator means for providing a NRRO compensation output having a first NRRO compensation gain adjusted when NRRO noise is above a noise threshold level, the compensator means providing the NRRO compensation output to the controller in a first preselected frequency band that corresponds with a first NRRO frequency peak. 
 
     
     
       26. The circuit of  claim 25  wherein the compensator means include a recursive algorithm that tunes the first gain control output in real time. 
     
     
       27. The circuit of  claim 26  wherein the recursive algorithm is a function of 
         g   ⁡     (   t   )       =     {                 α   *     ⁢     g   ⁡     (     t   -   1     )         +       β   *     ⁡     (          e        -     e   0       )         ,       when   ⁢           ⁢        e          >     e   0                         α   *     ⁢     g   ⁡     (     t   -   1     )         ,           ⁢       when   ⁢           ⁢        e          ≤     e   0         ⁢                         
 
       where t is a number of a time increment, g is the first gain, α has a value between 0 and 1, β is a tuning rate greater than 0, e is the first filter output and e 0  is a selected level of e for turning the automatic tuning on and off. 
     
     
       28. The circuit of  claim 27  wherein the recursive algorithm has an initial condition value g(0) at the start of a seek operation, and the initial condition value g(0) is adjusted as a function of track number.